Science Drivers

E3SM v3 will implement a three-pronged strategy for advancing Earth system modeling for actionable science:

• applying high-resolution models,
• representing human–Earth interactions, and
• quantifying uncertainty.

During Phase 1 and Phase 2 (first two funding cycles, in which E3SM v1 and E3SM v2 were developed), significant progress has been made in high-resolution modeling through simulations using a global high-resolution model configuration at 25 km and simulations using a North America regional refined mesh configuration featuring 25 km grid spacing over North America and the surrounding oceans for providing regional-scale climate information. Important progress has also been made in modeling the coupled human–Earth system through coupling of E3SM with the Global Change Assessment Model (GCAM), enabling the development of energy-relevant scenarios and analysis of the effectiveness and consequences of climate mitigation and adaptation options. While high-resolution modeling and human–Earth system modeling will remain high priorities,  E3SM v3 will further advance actionable science by addressing uncertainty in future projections. A common science question to address is the contribution of different sources of uncertainty to the total uncertainty in future projections of societally relevant outcomes. Examples of societally relevant outcomes include energy- and water-security impacts from climate change, especially changes in extreme events and coastal resilience against regional sea level rise.

By addressing model biases, quantifying uncertainty, and understanding the sources of uncertainty, the project will advance our goal of providing credible, actionable projections of regional climate change to support decision making. Below, the science questions and science goals are discussed in the context of each science driver and associated actionable outcomes. 

E3SM’s overarching science goal is to advance actionable science in support of DOE’s energy mission

Overarching science questions

What are the relative contributions of model parametric uncertainty and internal variability to uncertainty in projecting future changes in water availability and water security, including the impacts of extreme events? 

• What is the contribution of internal variability to the total uncertainty in projections of water availability in US river basins? Which modes of variability dominate the uncertainty associated with internal variability?
• How do biases in the Atlantic Meridional Overturning Circulation and Aerosol Cloud interactions, the two dominant biases in E3SMv1 and v2, influence the model water cycle response to external forcing? For example, what are the specific roles of resolved mesoscale eddies and air–sea fluxes in the AMOC biases and model uncertainty?
• What mechanisms may connect model parametric uncertainty and internal variability and influence the total uncertainty in projecting future changes in water availability and water security? 

Science goals 

• Mitigate critical, persistent biases in E3SM v1 and v2 (most notably the weak AMOC and strong response to aerosol forcing).
• Advance the development of large ensemble simulations spanning model parametric uncertainty and internal variability for actionable simulations and projections to support energy mission.
• Advance the usability of E3SM RRM and the multiscale modeling framework (MMF or superparameterization) for the simulation campaigns and the broader community. 

Overarching science questions

What are the impacts of different US decarbonization scenarios on US regional climate and evolution of the human– Earth systems? 

• How do different pathways of energy futures contribute to the US decarbonization scenarios? What factors contribute to uncertainty in the decarbonization pathways?
• What are the implications of decarbonization on the biogeochemical (carbon, methane, nitrogen, and phosphorous) cycles through land use and land cover change, land management, greenhouse gas and aerosol emissions, and sediment and nutrient input to the ocean and subsequent changes in ocean biogeochemistry?
• How do different decarbonization scenarios influence US regional climate change and populations exposed to heat extremes and wildfires? 

Science goals

• Advance modeling of human–earth interactions to support actionable science for energy mission.
• Address uncertainty in decarbonization pathways.
• Advance understanding of the impacts of different decarbonization pathways. 

Overarching science questions

What polar processes and their model representations contribute to key uncertainties in projecting regional sea level rise? 

• How do uncertainties in modeling mass loss from the Greenland and Antarctic ice sheets contribute to uncertainty in projecting regional sea level rise?
• How is uncertainty in modeling the mass loss (and hence sea level rise) from Greenland and Antarctica partitioned between uncertainty in modeling climate processes (e.g., internal variability, emissions scenario, model biases) and uncertainty in modeling ice sheet processes?
• What are the impacts of model polar climate biases on global climate through teleconnections and feedbacks? 

Science goals

• Advance modeling of mass loss from the Greenland and Antarctic ice sheets.
• Address the role of polar biases in modeling global climate. 

E3SM v4 is poised to be a transformative modeling tool for answering scientific and societally relevant questions about regional and global climate change and its impacts.

DRIVER: Water Cycle Changes and Impacts.

Floods and storms contribute disproportionately to natural disaster events worldwide, with large socio-economic impacts.

Overarching science question.

What are the impacts of future changes in extreme events and water availability on the human populations and ecosystems in vulnerable regions?

DRIVER: Human-Earth System Feedbacks.

Different energy pathways for net-zero greenhouse gas emissions will have important implications for Earth and environmental changes. On multi-decadal-to-century timescales, biogeochemical cycle feedbacks play an important role in mapping the energy pathways and Earth system changes, with consequential impacts on the well-being of the global human populations and ecosystems.

Overarching science question.

What are the impacts of biogeochemical cycle feedbacks on the climate and societal outcomes of different energy pathways to reach net-zero greenhouse gas emissions?

DRIVER: Polar Processes, Sea-Level Rise and Coastal Impacts.

Rapid sea level rise resulting from marine ice sheet instability and ice shelf instability has consequential impacts on coastal communities. However, if and when such instabilities will occur in the future represents the single largest uncertainty in projecting future sea level rise. Similarly, the timing and seasonality of total sea ice depletion in the Arctic is subject to considerable uncertainty yet is important for US energy policy and sovereignty.

Overarching science question.

What is the likelihood of rapid sea level rise due to tipping points induced by marine ice sheet instability and ice shelf instability and the likelihood of total Arctic sea ice loss spanning more than a month of each year from the present out to 2060? 

From the inception, the E3SM project’s scientific development was dictated by three science drivers, that in Phase 1 and  Phase 2 of the project were more general and relate to water cycle, biogeochemistry, and cryosphere systems.

E3SM Phase 1 and Phase 2 (E3SM v1 and v2) Science Questions